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Share-MDT-based delivery
A share-MDT can be used for delivering multicast packets, including both multicast protocol packets and
multicast data packets. However, the transmission processes for these two types of multicast packets are
different.
Delivery of multicast protocol packets
To forward the multicast protocol packets of a VPN over the public network, the local PE device
encapsulates them into public-network multicast data packets. These packets are transmitted along the
share-MDT, and then de-encapsulated on the remote PE device to go into the normal protocol procedure.
Finally a distribution tree is established across the public network.
The following describes how multicast protocol packets are forwarded in the following circumstances:
•
If the VPN network runs PIM-DM or PIM-SSM:
{
Hello packets are forwarded among MTI interfaces to establish PIM neighboring relationships.
{
A flood-prune process (in PIM-DM) or a join process (in PIM-SSM) is initiated across the public
network to establish an SPT across the public network.
•
If the VPN network runs PIM-SM:
{
Hello packets are forwarded among MTI interfaces to establish PIM neighboring relationships.
{
If the receivers and the VPN RP are in different sites, a join process is initiated across the public
network to establish an RPT.
{
If the multicast source and the VPN RP are in different sites, a registration process is initiated
across the public network to establish an SPT.
•
If the VPN network runs BIDIR-PIM:
{
Hello packets are forwarded among MTI interfaces to establish PIM neighboring relationships.
{
If the receivers and the VPN RP are in different sites, a join process is initiated across the public
network to establish the receiver-side RPT.
{
If the multicast source and the VPN RP are in different sites, multicast data is transmitted across
the public network to establish the source-side RPT.
NOTE:
All interfaces that belong to the same VPN, including those interfaces with VPN instance bindings and the
MTI on PE devices, must run the same PIM mode.
The following example explains how multicast protocol packets are delivered based on the share-MDT
when PIM-SM is running in both the public network and the VPN network, with receivers and the VPN RP
located in different sites.
As shown in
, PIM-SM is running in both the public network and the VPN network, Receiver for
the VPN multicast group G (225.1.1.1) in Site 2 is attached to CE 2, and CE 1 of Site 1 acts as the RP for
group G (225.1.1.1). The share-group address used to forward public network data is 239.1.1.1.
